The present invention relates to fiber optic networks, and more particularly to light sources in a fiber optic network.
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high data capacity capabilities. In response to the demand for ever higher capacity fiber optic networks, network components are designed to provide increasingly broad bandwidths. As the number of wavelengths increases, so does the demand on the number of lasers required to maintain a laser source system in a network.
FIG. 1 illustrates one type of conventional laser source system. Assume that a fiber optic cable comprises ten parallel optical fibers, each associated with exactly one wavelength division multiplexer (WDM) system 102a-102j, respectively Each system comprises n wavelengths. Conventionally, one laser light source is used for each wavelength in a system. Thus, for n wavelengths in system 102a, n lasers 104.1-104.n are required; for the same n wavelengths in system 102b, n lasers 106.1-106.n are required; and for n wavelengths in system 102j, n lasers 108.1-108.n are required. For example, if each system comprises 64 wavelengths (that is, n=64), with ten systems, the fiber optic cable requires 640 lasers.
As the number of channels in data communications systems increases, the pass bands the wavelengths become narrower, placing more stringent requirements on the lasers"" precision. Instability and imprecision can be caused by drift, mode hopping, and crosstalk, for example. Drift refers to the difference between an actual wavelength and the wavelength at the center of the pass band. If drift occurs, crosstalk between channels will be too large. Crosstalk occurs when one channel or part of a channel appears as noise on another adjacent channel. Mode hopping occurs when a laser randomly oscillates among permitted cavity modes of slightly different wavelengths. By using one laser per wavelength per system, each laser may be designed to provide a particular wavelength in a very stable manner with uniform intensity. However, lasers are expensive and must be selected for desired wavelength after manufacture and the requirement of one laser per wavelength per system burdens the network operator with high costs. Also, with so many lasers in different locations, maintenance and service of the lasers are expensive and time consuming.
One conventional way of decreasing this burden is illustrated in FIG. 2. FIG. 2 illustrates a centralized laser source transmission system. With this type of system, one high powered laser is used for each wavelength. The optical power from each laser is split among the systems in the cable. For example, assume the cable has ten parallel optical fibers each associated with exactly one WDM system 202a-202j respectively, and that each system comprises n wavelengths. For n wavelengths, n lasers 204.1-204.n are used, each emitting a single wavelength at ten times the power normally required. The power from laser 204a is split ten ways among the systems 202a-202j. The same is true for the wavelengths from lasers 204.2-204.n. Thus, for systems comprising 64 wavelengths each, instead of requiring 640 lasers as with the network illustrated in FIG. 1, the network in FIG. 2 only requires 64 lasers. Although this reduces the cost for lasers, there is a cost involved in providing high power at each wavelength. The maintenance and service of this number of single wavelength lasers is still costly and time consuming.
Accordingly, there exists a need for a multi-wavelength light source for a fiber optic network. The light source should not compromise the stability of the wavelengths. It should reduce the costs of operating and maintaining the network. The present invention addresses such a need.
The present invention provides a light source for an optical network. The light source includes a semiconductor optical gain element, having an axis of symmetry; and a mechanism for reflecting wavelengths that correspond to optical transmission channels of the optical network, the reflecting means optically coupled to the semiconductor optical gain element and intersecting the axis of symmetry. The light source of the present invention is a single multi-wavelength light source. It is designed to only emit wavelengths that specifically correspond to optical transmission channels. The mechanism of the light source suppresses possible mode hopping, thus maintaining the power stability of all channels. Since multiple wavelengths are provided in a single light source, the number of lasers required to service a network can be dramatically reduced, increasing efficiency and reducing the cost of equipment and time for maintenance as well.